The most commonly used procedure for the manufacture of continuous fiber product, such as strand, consists of drawing streams of attenuable material in attenuable condition, such as molten glass, from a bushing, the base of which is equipped with orificed tips. When cooling means are associated with the tips, stable separation of the streams in enhanced. The tips tend to minimize the phenomenon of "flooding" of the bushing base particularly at the time of a filament rupture during the fiberization operation. This flooding is manifested by the tendency of the molten material issuing from an orifice to spread over the surrounding undersurface of the base plate because of capillary action and the wetting effects of the plate. At the moment of filament rupture during the fiberization operation, the presence of tips tends to reduce the massive flooding of the base plate which would otherwise occur.
Taking into account the difficulties in manufacturing a bushing base with tips and also the significant surface area occupied by the tips, various efforts have been made to eliminate them and to replace the tipped bushing base with a generally flat perforated plate having a large number of orifices within a given surface area. The result of these efforts is the simultaneous attenuation of a larger number of filaments per bushing and consequently the possibility of the manufacture of new products, and a reduction in deformation problems of the bushing base which become progressively more significant as bushing surface area becomes larger.
Numerous techniques, as described in the co-pending applications, have been proposed in an effort to reduce the tendency towards flooding of non-tipped bushings, and thereby to attempt to reduce the problems inherent in establishing conditions suitable for fiberizing after such flooding.
The foregoing co-pending application Ser. No. 207,712 discloses method and apparatus for obtaining controlled and stable flooding confined to well defined areas instead of working towards reducing the tendency towards flooding. These areas are located in the bushing bottoms and are perforated with a plurality of orifices arranged to facilitate restarting. According to application Ser. No. 207,711 a bushing is provided with elongated hollow channels, separated by downwardly open grooves in which cooling fins, located lengthwise of the channels, may be mounted. The bottom walls of the channels have orifices which are desirably provided in at least two spaced parallel rows. Bushings of the kind just described are both characterized by their capability of reducing temperature differences existing at the exits of the orifices to very small values. Because of this temperature stability, fiberization can be carried out with relatively few interruptions and very fine fibers of uniform diameter can be produced.
According to the invention disclosed in application Ser. No. 207,712, series of bosses which define cells or alveoles are disclosed. The bottom walls of the bosses are substantially continuous having a plurality of orifices in communication with each alveole. According to application Ser. No. 207,712 the region of the bottom wall in communication with each alveole is flooded and fiberization of the glass may proceed selectively either into a single fiber from each alveole or into as many fibers as there are orifices in communication with each alveole. Bushings described in U.S. application Ser. No. 207,712 have the capability of making strand comprised of fibers of different sizes. The bushings are easy to start up and to restart in the event of filament rupture.
The bushings described in both applications are characterized by having a large number of orifices per unit of surface area, a large total number of orifices per bushing, and good fiberization stability, even for the manufacture of filaments of small diameter.